Glucose Metabolism and Energy Pathways

Glycolysis - where

Cytosol of all cells

Glycolysis - trigger

Insulin (high blood glucose)

Glycolysis - 3 key (irreversible) enzymes

Hexokinase/glucokinase; phosphofructokinase; pyruvate kinase

Glycolysis - net yield per glucose

2 pyruvate; 2 ATP; 2 NADH

Glycogenesis - where

Liver and muscle cytoplasm

Glycogenesis - trigger

Insulin

Glycogenesis - key enzyme

Glycogen synthase (activated by insulin)

Glycogenesis - enzyme that traps glucose

Hexokinase (muscle) or glucokinase (liver)

Glycogenolysis - where

Liver and muscle cytoplasm

Glycogenolysis - trigger in liver

Glucagon

Glycogenolysis - trigger in muscle

Epinephrine (and cortisol)

Glycogenolysis - key enzyme

Glycogen phosphorylase

Glucose-6-phosphatase

Liver-only enzyme that makes free glucose so it can enter the blood

Why muscle can't raise blood glucose

Muscle lacks glucose-6-phosphatase

Gluconeogenesis - where

Liver

Gluconeogenesis - trigger

Glucagon; cortisol; epinephrine; norepinephrine (low blood glucose)

Gluconeogenesis - starting materials

Lactate; glycerol; amino acids

Gluconeogenesis - 4 bypass enzymes

Pyruvate carboxylase; PEP carboxykinase; fructose-1.6-bisphosphatase; glucose-6-phosphatase

Lactate dehydrogenase

Pyruvate + NADH makes lactate + NAD+; regenerates NAD+ so glycolysis continues without O2

Cori cycle

Muscle glycolysis makes lactate; liver gluconeogenesis turns it into glucose; stimulated by anaerobic exertion

Transition step - enzyme and location

Pyruvate dehydrogenase; mitochondrial matrix

Transition step - products

Acetyl-CoA + CO2 + NADH

Krebs cycle - start and location

Acetyl-CoA + oxaloacetate makes citrate; mitochondrial matrix

Krebs cycle - waste product

CO2

ETC - location and carriers

Inner mitochondrial membrane; NADH and FADH2 bring electrons

ETC - how ATP is made

H+ is pumped across the membrane; H+ flows back through ATP synthase to make ATP; O2 is the final acceptor and forms H2O

Total ATP per glucose (your slide)

38 ATP (NADH = 3 ATP; FADH2 = 2 ATP)

Insulin vs glucagon

Insulin = high blood glucose; stores (anabolic); glucagon = low blood glucose; mobilizes (catabolic)